Diagnosing diseases of the cardiopulmonary system is one of the most frequently posed problems in medicine. For example, prior to an operation under anesthetic, investigations must be carried out to determine the patient's cardiopulmonary status. This is done in most cases on the basis of X-ray images. Consequently, the chest X-ray is the most frequent radiological examination of all.
Chest X-ray examination can be used to answer a large number of medical questions with varying degrees of success. This examination is expected to produce findings concerning the patient's cardiac function, e.g. whether signs of congestion of the pulmonary vessels are visible. It is also expected to provide indications of malignant diseases, such as so-called circular foci. Chest X-ray examination can also be used to detect infectious lung diseases such as pneumonia. Findings in respect of obstructive and restrictive lung diseases and indications of effusions are also possible. Chest X-ray examination has the particularly advantage of being inexpensive.
However, the chest X-ray method also has a number of disadvantages, chief among them being the patient's radiation load. Also the diagnostic value is low for some questions. For example, signs of congestion are a very indirect and only subjectively evaluable parameter in the X-ray photograph. Even obstructive and restrictive diseases are only detected indirectly and subjectively by a reduction or increase in lung marking. Moreover, chest X-ray examination does not allow quantifiability of results. Lastly, chest X-ray photographs are only comparable to a limited extent, as the visual appearance depends e.g. on the exposure and also on the depth of inhalation. Because of the large range of features to be evaluated, the examiner must be very experienced with such photographic images in order to make any kind of reliable assessment. On the other hand, the radiologist has to evaluate a large number of images daily, the danger being that indications of diseases will be overlooked in one image or another.
A number of methods are now known which enable the abovementioned diseases to be better and more accurately detected than by chest X-ray. For example, heart diseases can be better and more accurately found using echo cardiography, i.e. an ultrasound examination of the heart. X-ray computed tomography likewise enables the condition of lung and heart to be imaged and also diagnosed with a high degree of accuracy. Finally, magnetic resonance imaging (MRI) permits excellent vascular analysis and soft tissue differentiation.
However, none these methods has been able to replace the chest X-ray. The main reason for this are the comparatively high costs of these alternative methods, which stand in the way of their being used routinely and therefore frequently. A significant portion of the examination costs comes from producing the images. For MRI, for example, particularly qualified personnel are required in order to carry out the examination so as to ensure high diagnostic quality. It is therefore desirable to make it attractive to use MRI also routinely as a more informative examination method than chest X-ray.
U.S. Pat. No. 6,411,088 (corresponding to DE 100 07 598 A1) discloses an MRI scanner for creating a radiological image. The scanner incorporates a C-shaped main field magnet system which is fixed to a wall of a room. To create a radiological image, a patient to be examined enters the side opening of the C-profile. The scanner is provided with handles so that, while the image is being taken, the patient is able to stand as still as possible by pulling or pressing against a surface designed for that purpose, thereby avoiding motion artifacts in the resulting image. The scanner also comprises a gradient coil system, an RF transceiver, a display and operator control device and a central control system which is appropriately connected to the gradient coil system, the RF transceiver and the display and operator control device. In particular, with the MRI scanner described there, refocused gradient echo sequences e.g. implemented as a true FISP sequence can be executed for the examination.
US patent application publication US 2003/0095696 A1 describes an apparatus and a method for computer-aided diagnosis of small pulmonary nodules. Two main steps are carried out for pulmonary nodule assessment. First the locations of possible nodules must be identified. This is followed in the next step by characterization to evaluate the possibility that a detected nodule contains cancer tissue. Characterization is based on the growth rate of the nodule, which requires comparing the sizes in two images taken at different times. A method of detection and feature extraction for size characterization is also described there.
US patent application publication US 2003/0068074 A1 describes a computer system and a method for segmentation for the purpose of imaging and quantifying the volume of the segmented region in digital images, wherein a watershed transformation of the digital image is performed. In post-processing, the picture elements which must be assigned to a least one catchment basin are implemented using grey value based segmentation, visualization by means of a transfer function or volume determination using histogram analysis.
A method for computer-aided detection of pulmonary nodules including these fed by vessels is known from U.S. Pat. No. 7,020,316 B2, wherein a seed point is automatically detected from a plurality of images. The seed point defines a volume of interest (VOI). Finally, the shape or outline of projections of the volume of interest is analyzed to detect nodules.